1. Field of the Invention
The present invention relates to a clock spring connector which is incorporated in a steering device of an automobile and used as an electrical connecting means for an air bag or the like.
2. Description of Related Art
In a clock spring connector, a fixed member is connected through a belt-like flexible cable to a movable member so mounted as to be rotatable relative no this fixed member. The clock spring connector is employed as an electrical connecting member between a movable member and a fixed member, having a finite number of revolutions as in the case of a steering device of an automobile.
In this clock spring connector, the flexible cable occupies a high percentage of the total cost. Proposed in the specification of U.S. Pat. No. 4,540,223 is a clock spring connector constructed to reduce the costs by decreasing the length of a flexible cable needed.
FIG. 10 is a plan view showing a schematic construction of a clock spring connector disclosed in the aforementioned specification. As shown in the same Figure, a movable member 101 is mounted to a cylindrical fixed member 100 so as to be rotatable relative to the fixed member 100. The fixed member 100 is fixed to a steering column of an automobile and the movable member 101 is fixed to a steering wheel. A ring-like incorporating space 102 is defined between the fixed member 100 and the movable member 101, and a flexible cable 103 is incorporated in the incorporating space 102. The flexible cable 103 is fixed to the fixed member 100 and the movable member 101, and introduced out of the incorporating space 102. The winding direction of the flexible cable 103 is turned back through a U-shaped turned-back portion 103a within the incorporating space 102. A C-shaped spacer 104 is disposed within the aforementioned incorporating space so that the spacer is movable along the periphery of the aforementioned incorporating space. The turned-back portion 103a of the aforementioned flexible cable 103 is looped on a roller 105 which is supported through a shaft on the opening end of the spacer 104.
For example, if the movable member 101 is rotated clockwise in FIG. 10 while interlocked with a handle, the turned-back portion 103a of the flexible cable 103 moves along the periphery of the incorporating space 102 so that the flexible cable 103 is rewound on the outer cylindrical unit of the fixed member 100 more densely than on the inner cylindrical unit. In reverse to this case, if the movable member 101 is rotated counterclockwise in FIG. 10, the turned-back portion 103a of the flexible cable 103 moves in the same direction so that the flexible cable 103 is wound on the inner cylindrical unit of the movable member 101 more densely than on the outer cylindrical unit. When the flexible cable 103 is wound or rewound, the spacer 104 receives a force from the turned-back portion 103a of the flexible cable 103 and the spacer 104 moves in the same direction.
In the clock spring connector having the aforementioned construction, the flexible cable 103 is wound on the inner and outer cylindrical units so that the winding directions of the flexible cable are opposite to each other. Thus, the length of the flexible cable can be remarkably decreased thereby reducing the costs as compared with such a clock spring connector in which the flexible cable is wound on the inner and outer cylindrical members in the same direction (in an eddy state). The C-shaped spacer 104 is disposed in the incorporating space 102 defined between the flexible cable 103 wound on the inner cylindrical unit and the flexible cable 103 wound on the outer cylindrical unit, and the turned-back portion 103a of the flexible cable 103 is looped on the opening end of the spacer 104. Thus, the spacer 104 is capable of restraining the flexible cable 103 from swelling along the radius until the cable which is wound on the outer cylindrical unit or the inner cylindrical unit reaches the turned-back portion 103 when the flexible cable is wound or rewound. Consequently, it is possible to feed the flexible cable 103 smoothly toward the turned-back portion 103a.
The clock spring connector having the aforementioned construction is subjected to various inspections before the connector is finally mounted in the steering device of an automobile, and the inspections include, for example, continuity inspection for the flexible cable 103, torque inspection of the movable member 101 or the like. If the movable member 101 is rotated until all the portion of the flexible cable 103 is rewound on the outer cylindrical unit of the fixed member 100, and further the movable member is excessively rotated in the same direction. The flexible cable 103 is turned back and buckled near the flexible cable extending portion of the movable member 101, so that the reliability of the connection is reduced.
Accordingly, the applicant of the present invention proposed a clock spring connector which is intended to prevent the flexible cable from being buckled. In the proposed clock spring connector, a sheet-like tongue piece is fixed to the flexible cable near the inner cylindrical unit. If the movable member is excessively rotated in the rewinding direction, the aforementioned tongue piece engages in between the opening end of the spacer and the inner cylindrical unit, as a supporting stick in order to block the movable member from further rotating.
However, because, in the clock spring connector of the prior art, the flexible cable is wound on the surface of the inner cylindrical unit against an elastic force of the sheet-like tongue piece, when the clock spring connector is assembled, the flexible cable wound on the surface of the inner cylindrical unit swells greatly by the elastic force of the tongue piece in such a direction that the flexible cable wound on the inner cylindrical unit comes into contact with the flexible cable wound on the surface of the outer cylindrical unit. As a result, it becomes difficult to install a spacer between both the flexible cables. Besides, because the tip of the tongue piece comes into contact with the spacer during the operation of the clock spring connector, the spacer may be restrained from rotating smoothly, thereby causing noises.